painting: when finding an end match, set its multidata right away

When leaving the multidata unset (as was done until now) and the
end match is offscreen, then this could lead to miscolorings later
when jumping over this end match instead of scrolling past it.

This fixes https://savannah.gnu.org/bugs/?60012.

Bug existed since before version 2.1.10.

src/winio.c

@@ -2500,7 +2500,7 @@ void draw_row(int row, const char *converted, linestruct *line, size_t from_col)
 				/* The match positions of a single-line regex. */
 			const linestruct *start_line = line->prev;
 				/* The first line before line that matches 'start'. */
-			const linestruct *end_line = line;
+			linestruct *end_line = line;
 				/* The line that matches 'end'. */
 			regmatch_t startmatch, endmatch;
 				/* The match positions of the start and end regexes. */
@@ -2720,7 +2720,16 @@ void draw_row(int row, const char *converted, linestruct *line, size_t from_col)
 				wattron(edit, varnish->attributes);
 				mvwaddnstr(edit, row, margin + start_col, thetext, -1);
 				wattroff(edit, varnish->attributes);
+
 				line->multidata[varnish->id] = STARTSHERE;
+
+				if (end_line->multidata == NULL) {
+					end_line->multidata = nmalloc(openfile->syntax->nmultis * sizeof(short));
+					for (short item = 0; item < openfile->syntax->nmultis; item++)
+						end_line->multidata[item] = 0;
+				}
+				end_line->multidata[varnish->id] = ENDSHERE;
+
 				break;
 			}
 		}